The first driver that worked for me was a Pegasus driver for Mac OS X 10.3 (Panther) developed by Daniel Sumorok. Since then I've been collaborating with Daniel to help make more drivers available. We have ported his original Pegasus driver to work on Mac OS X 10.4 (Tiger or later), and developed a USB 2.0 AX8817x driver. All are open source released under a GPL license.
You can download them from here:
The Pegasus chipset provides a USB 1.1 compatible implementation which could be a concern for some users. USB 1.1 runs at 1.5 Mbps (low speed) or 12 Mbps (full speed). For best performance, it's important to isolate any low speed devices on a separate bus. Mice and keyboards often run at low speed.
Using the Link Rate tool in IPNetMonitorX, I measured the link rate to another device on my LAN as 6 Mbps. The built-in Ethernet on my 12" PBG4 reported 44 Mpbs. When I measured the link rate to the next hop router through my cable modem, it reported 1 mbps. It didn't make any difference whether I used Ethernet built-in or the USB-To-Ethernet adaptor. Finally, I downloaded a 2.2 MB file to compare the throughput using the Monitor tool.
Both downloads took 5 seconds, but Ethernet built-in reached a peak rate of 589 KBps versus 579 kBps. Repeating the experiment several times produced similar results. Ethernet built-in might be 1-2% faster, but performance was clearly limited by the speed of my cable modem (Your Mileage May Vary).
USB 2.0 Performance
The AX8817x chip set provides a USB 2.0 compatible implementation which runs at up to 480 Mbps (high speed), so it should be possible to keep up with 100 Mbps fast ethernet as long as there are no other slower devices on the same bus. To test this I copied a 64.8 MB music file to my PBG4 laptop connected through a LinkSys USB200M Ethernet Adaptor (en3) and compared this to the same file transfer using Built-in Ethernet (en0).
Both transfers reached 10 MBps (80-90 Mbps) and took about 10 seconds. I repeated the test in the other direction.
While the USB-To-Ethernet adaptor was slightly slower, at 80 Mbps there was little noticeable difference. Files moved quickly from one system to another via 100 Mbps fast Ethernet. Copying the same file using AirPort wireless took 50-90 seconds.
Stability
While other USB-To-Ethernet drivers are reported to be buggy, I haven't encountered any stability problems to date. The adaptor turns off when the computer goes to sleep and comes back on when the computer awakes. It does not support "Wake On LAN" at this time.
Wrap Up
This USB-To-Ethernet Adaptor combination could be an attractive solution for a Mac Mini, or old iBook used as an Internet gateway or server. I'm particularly fond of using old laptops as servers since they are compact, quiet, use little energy, and include their own battery backup.
Read more: http://mac.softpedia.com/get/System-Utilities/USB-to-Ethernet.shtml#ixzz4HT31r53P